Tissue may be destroyed, ablated, or otherwise treated using thermal energy during various therapeutic procedures. Many forms of thermal energy may be imparted to tissue, such as radio frequency electrical energy, microwave electromagnetic energy, laser energy, acoustic energy, or thermal conduction. In particular, radio frequency ablation (RFA) may be used to treat patients with tissue anomalies, such as liver anomalies and many primary cancers, such as cancers of the stomach, bowel, pancreas, kidney and lung. RFA treatment involves destroying undesirable cells by generating heat through agitation caused by the application of alternating electrical current (radio frequency energy) through the tissue.
Various RF ablation devices have been suggested for this purpose. For example, U.S. Pat. No. 5,855,576 describes an ablation apparatus that includes a plurality of electrodes (tines) deployable from a cannula. Each of the electrodes includes a proximal end that is coupled to a generator, and a distal end that may project from a distal end of the cannula. The electrodes are arranged in an array with the distal ends located generally radially and uniformly spaced apart from the distal end of the cannula. When using the above described devices in percutaneous interventions, the cannula is generally inserted through a patient's skin, and the tines are deployed out of the distal end of the cannula to penetrate target tissue. The electrodes are then energized to ablate the target tissue. The electrodes may be energized in a bipolar mode (i.e., current flows between closely spaced electrode) or a monopolar mode (i.e., current flows between one or more electrodes and a larger, remotely located common electrode) to heat and necrose tissue within a precisely defined volumetric region of target tissue.
Ablation devices have also been implemented using catheters. Physicians make use of catheters today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances. During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician places an ablating element carried on the catheter near the cardiac tissue that is to be ablated. The physician directs energy from the ablating element to ablate the tissue and form a lesion. Such procedure may be used to treat atrial fibrillation, a condition in the heart in which abnormal electrical signals are generated in the endocardial tissue.
Ablation catheters typically have an elongated shaft carrying an electrode at its distal end. Lesions of different shapes and sizes may be formed by choosing a suitable electrode shape or size, and/or by manipulating the position of the electrode at the distal end of the catheter. An ablation catheter may also have a steering mechanism for steering its distal end, which is beneficial because it allows a physician to steer the catheter through veins and vessel junctions. It also allows the physician to accurately position the electrode carried at the distal end at a target site to be ablated. Steerable ablation catheters have been described in U.S. Pat. Nos. 6,033,378 and 6,485,455 B1, the disclosures of which are expressly incorporated by reference herein.
During use of an ablation device, the electrode delivering ablation energy may overheat, thereby causing tissue charring and preventing formation of a deeper lesion. This may negatively affect the ablation catheter's ability to create a desirable lesion. An overheated electrode may also cause healthy tissue adjacent the target site to be heated. Furthermore, an overheated electrode may cause blood to be heated, thereby creating an undesirable embolism. As such, an ablation device that is capable of cooling an electrode is very desirable.
Ablation devices that have cooling capability are generally connected to a pump via a fluid delivery tube. The pump delivers cooling fluid to the ablation device for cooling an electrode on the ablation device. However, cooling systems that require use of the pump and the fluid delivery tube may be expensive to design and implement, and may be inconvenient and a nuisance to use. For examples, during an operation, the fluid delivery tube connecting the pump and the ablation device may tangle with another medical equipment, or may interfere with the operation. Also, the pump may produce noise that interfere with a physician's concentration, and may disturb conversation between operators in the operation room. In addition, fluid may leak at the pump, at the fluid delivery tube, or at the ablation device. Further, for steerable ablation catheters, if not designed or constructed properly, the fluid delivery tube inside the catheter may kink or buckle during use. For the foregoing reasons, cooling an electrode using fluid delivered from a pump may not be desirable.
Thus, there is currently a need for an improved ablation device that is capable of cooling an electrode during use. Also, it would be desirable that such ablation device does not require use of a pump.